Gastroesophageal reflux disease (GERD) is a condition in which the contents of the stomach flow back (reflux) into the esophagus and damage its lining. GERD occurs when the lower esophageal sphincter (LES), which separates the esophagus and stomach, does not close properly and/or is weak.

The esophagus carries food from the mouth to the stomach. The LES is a group of muscles that serves as a valve between the esophagus and stomach. When food reaches the LES, the LES relaxes and allows it to enter the stomach. After food enters the stomach, the LES contracts to prevent food and other stomach contents from backing up into the esophagus.

When the LES is weak or remains relaxed for too long, contents of the stomach can reflux into the esophagus. The tissue lining the esophagus differs from the stomach lining and is more susceptible to acid. This causes a burning sensation in the chest or throat called heartburn. When stomach acid can be tasted in the back of the mouth, it is called acid indigestion. In some people, reflux affects the vocal cords or causes stomach contents to flow into the lungs (aspiration).

Experiencing some degree of reflux after a meal is normal. In most people, episodes are brief and do not produce symptoms. Occasional episodes of heartburn are also common in healthy people. Having heartburn does not necessarily mean that a patient has GERD. Patients with GERD experience heartburn and other symptoms more frequently than others and may have damage to the esophagus.

Most patients with GERD, especially those who receive treatment for the condition, will not experience complications. However, GERD can cause a variety of complications including:

• Ulcers in the esophagus. Inflammation of the esophagus (esophagitis) can lead to ulcers, which may be accompanied by bleeding.
  
  
• Stricture. Stomach acid can cause the esophagus to scar and narrow. This can result in pills or food getting stuck.
  
  
• Lung and throat problems. Stomach acid can cause inflammation of the vocal cords (laryngitis), resulting in a sore throat or a hoarse voice. Acid in the lungs can result in asthma symptoms or aspiration pneumonia. Chronic acid reflux can result in permanent lung damage, a condition called pulmonary fibrosis or bronchiectasis.
  
  
• Barrett's esophagus. A few people with GERD may develop this precancerous condition in which the cells lining the lower part of the esophagus are changed or replaced with abnormal cells. An even smaller number of patients with GERD develop adenocarcinoma, a type of esophageal cancer.

GERD can affect anyone, including infants and children. In children, it can cause repeated vomiting, coughing and other respiratory problems. It is usually caused by an immature digestive system and most infants outgrow the condition in their first year.